The field of this invention relates to a flow control valve to be usable in conjunction with a flexible walled tube to regulate the rate of flow of fluid through the tube.
In the administration of fluid into a human body for a medical purpose, it is customary to store a quantity of the fluid that is to be supplied to the human body within a container such as a bottle, plastic bag or other similar container. The typical way in which this is supplied to the human body is intravenously. The typical way that the fluid is administered intravenously is that the container is located at a height greater than the patient. The fluid within the container is then permitted to flow by gravity through a flexible walled tube and through a needle which has been entered within a vein of the human being. It is common for the patient's physician to require that the contained fluid be incrementally metered to the patient in terms of a given number of drops of fluid per minute. With adults, this number of drops per minute can be very small and with pediatric patients, the flow rate can be even smaller.
In the past, there has been utilized in conjunction with the tubing a pinch valve assembly which would pinch a portion of the tubing in order to meter the amount of fluid being given to the patient. Such pinch valves usually utilize a roller which presses against the tubing. It has been found that when this roller is set to administer to the patient a certain number of drops per minute of the liquid, that it doesn't take long, such as within fifteen or twenty minutes, that this number of drops per minute is increased. As a result, within a hospital, it is common practice for a nurse to continuously move from patient to patient constantly checking such valves to make sure that the flow rate is maintained at its precise established level. For example, if a patient is being administered with thirty drops per minute of fluid, it doesn't take much of a movement within the valve to result in the patient receiving forty to fifty drops per minute.
The reason in the past that conventional valves have been difficult to be set and remain set is that the valve itself is encountering continuous pressure by the fluid pressing against the valve. This continuous pressure, though small, over a period of time will cause the valve to actually move a minute amount. This is referred to as "creep". It does not take much of an amount of movement to result in a substantially increased percentage of flow into the patient.
Additionally, the flexible walled tubing, which is usually formed of plastic, has an inherent characteristic of wanting to return to its original shape rather than its "pinched" configuration. This tendency to return to its original shape is referred to as "cold flow" of the material. Because of this "cold flow" and "creep", conventionally used valves are just not capable of precisely regulating over a period of time the amount of fluid that is being administered to a patient.
The use of such a valve in conjunction with intravenous feeding equipment in the past has been rather an inexpensive part of the equipment. At the most, such a valve would cost only a few dollars. However, if a hospital wished to insure that a patient was receiving a precisely controlled amount of fluid, it was necessary for the hospital to purchase a flow regulating monitoring apparatus which was quite complicated. There is no doubt that such a monitoring apparatus would precisely control the flow of fluid to a patient and such devices are frequently used in a life-threatening situation. However, such devices are quite expensive. It would be most desirable if an inexpensive type of valve could be manufactured which would be able to achieve the high degree of precision of the expensive flow monitoring apparatuses which are now in current widespread use within hospitals.